This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 198 34 674.3 filed in Germany on Jul. 31, 1998; the entire content of which is hereby incorporated by reference.
The invention generally relates to the provision of a temporary selective national roaming at predetermined network operation conditions, e.g. at network overload in a mobile radio communication system. In particular, the invention relates to a method, an exchange, a telecommunication system and a mobile station of a mobile radio communication network, wherein one or more mobile stations of a first mobile radio communication network are transferred to a second mobile radio communication network, when an overload condition occurs in the first mobile radio communication network. There is also the possibility that the mechanism is invoked by maintenance personnel, e.g. due to some very severe maintenance activities or at an exchange or network failure.
FIG. 4 shows an overview of a nationwide telecommunication system TELE, where several mobile radio communication networks HPLMN, VPLMN1, VPLMN2 . . . VPLMNn (e.g. a D1, D2 or E-Plus network) can co-exist. Whilst FIG. 4 shows the co-existence of the networks, it should be understood that, of course, geographically the networks may cover the same geographical areas. Each mobile station MS (or generally a subscriber station) has a particular subscription to one of the networks. Such subscription data is stored in the home location register HLR. The mobile stations MS are served by respective switching means MSC/VLR within the networks. The switching means comprises the mobile switching center MSC and a visitor location register VLR. Other means necessary for forming the communications between the mobile station MS and the switching center MSC/VLR, like the base station controllers BSCs, the base transmitter stations BTS and the base stations BS, of the individual networks are not illustrated in FIG. 4, however, of course, it is assumed that the communication between the mobile station MS and the switching means MSC/VLR and the home location register HLR is performed as in any standard GSM network. Since all mobile radio communication networks and the mobile stations themselves must comply with the GSM standard (or any other nationwide standard), of course, the mobile stations MS, MSxe2x80x2 can in principle perform communications in every network.
When quality of service of a mobile network is below an acceptable level due to lack of resources in the network, the network is considered to be in an overload condition. The resources can consist of processing power, memory, switching, radio or other resources. In such an overload condition, two serious traffic conditions can occur. Firstly, the complete network traffic handling capability may collapse such that all mobile stations currently registered within this network will have very poor grade of service from the network. Secondly, if a mobile station is just about to register in the network, its call setup request may be rejected. In this condition, the mobile stations can normally only perform emergency calls (112) and nothing else. In one alternative solution, currently supported by GSM, it is conceivable that the mobile station is adapted to select one of several networks through a key and a display on the mobile station, in which case the operator of the mobile station may manually select a new network once its call setup request has been rejected by the network. If the other network does not support the mobile station even temporarily then no further communication is provided for said mobile station, since either national roaming is not allowed or the second network has a high load due to many mobile stations attempting to select this network.
In a conventional mobile radio communication network according to the GSM standard, some provisions to handle overload conditions are made.
Firstly, there is the possibility to reduce the load in the network simply by restricting accesses from mobile stations, e.g. to simply reject further call setup requests by mobile stations which would cause a collapse of the network. The procedure as described in the ETSI GSM standard 08.08 (digital cellular telecommunication system (phase 2+), mobile-services switching center-base station system (MSC-BSS) interface; layer 3 specification) section 3.1.12.3, November 1996 and ETSI GSM 02.11 version 5.0.0 (digital cellular telecommunication system; service accessibility) section 4, November 1996, can be used. In such a procedure, an access of mobile stations to the network is restricted based on the so-called access classes of the subscribers. The ETSI GSM standards define access classes for particular groups of subscribers in accordance with the defined subscriptions. For example, access classes can be grouped according to the subscribed tariffs, such that an access to the network may be blocked for the group of private users whilst a group of business users may still obtain an access. Other definitions of the groups of subscribers or access classes are possible. During an overload condition, the subscribers belonging to one particular access class will not receive a service, if they are registered in their home public land mobile network HPLMN (see FIG. 4). If in such a situation there are no further services offered to this group of subscribers, they will not have service, sometimes not even an emergency service, since in GSM it is possible to define with the above-stated mechanism whether normal users are allowed to make emergency calls or not.
Rather than just completely rejecting an access to the network, another option to use in GSM is the national roaming option described in the ETSI GSM standard 03.22 version 5.2.0 (digital cellular telecommunications system (phase 2+); functions related to mobile stations (MS) in idle mode and group receive mode), August 1997. By contrast to the international roaming service, which is a service whereby a mobile station from a mobile network is able to obtain a service from a mobile network of another country that has a roaming agreement with the home network (when the roaming is allowed for the subscriber) the national roaming service is a service, whereby a mobile station of a given mobile network is able to obtain a service from another mobile network in the same country, anywhere or even on a regional basis. The availability of national roaming depends on the home mobile network and the visited mobile network and does not depend on the subscription arrangements.
Essentially, as is shown in FIG. 4, during an overload condition the mobile station MS can roam to another network VPLMN1 (hereinafter called the visited or second network) in the home PLMN country. When this mobile station MSxe2x80x2 is temporarily served by the switching means MSC/VLR of the visited network VPLMN1, the mobile station will periodically perform attempts to register back to its home network HPLMN. If several visited networks VPLMN1, VPLMN2 . . . VPLMNn exist, the mobile station MS may attempt to gain an access in a particular network.
FIG. 5 shows the national roaming service for a group of mobile stations MS1, MS2, MS3, MS4 served by a switching means MSC1 of the network HPLMN. As shown in FIG. 5, two switching means MSC1, MSC2 of two location areas LA1, LA2 respectively serve a number of mobile stations. The location area LA of the visited network VPLMN geographically overlaps with some of the location areas of the home network HPLMN. If a mobile station does not get service in the home network HPLMN, e.g. in the overload area OVLD-AR, the mobile stations MS1-MS4 attempt to roam into one of the switching means MSC1xe2x80x2, MSC2xe2x80x2 of the visited network VPLMN, depending on at which location area of the VPLMN they are at the moment. Of course, the switching means MSC1xe2x80x2, MSC2xe2x80x2 may already be serving some mobile stations MS1xe2x80x2-MS4xe2x80x2, which have a subscription in the visited network VPLMN (It is noted that, e.g. GSM 03.02,5.1.0, May 1996, defines as MSC area the part of the network covered by an MSC which may consist of one or more location areas, such that one LA is only served by 1 MSC).
Whilst the national roaming service in principle allows a mobile station, which can currently not be handled within its own home network HPLMN, to access a visited network VPLMN, the disadvantage is that the number of mobile stations cannot be controlled more than on a regional basis; i.e. the mobile stations MS1-MS4 will access the switching means MSC1xe2x80x2, MSC2xe2x80x2 which is serving their present location.
If the home network HPLMN goes down, especially due to the overload condition, and some or all mobile stations are allowed to roam to another network VPLMN according to their own choice, this may cause a high traffic and even the new network VPLMN or all other networks VPLMN1, VPLMN2 . . . VPLMNn might end up in a severe overload condition. For example, in FIG. 5 the switching means MSC1xe2x80x2 of the visited network VPLMN in the location area LA might immediately become overloaded when all mobile stations MS1-MS4 simultaneously decide to temporarily roam to this switching means. On the other hand, some of the mobile stations, which are the first to request an access in the visited network VPLMN, may still be served, whilst those mobile stations, which only later request an access, will be rejected. Thus, there is no guarantee that the mobile stations which have already been rejected by their home network will be handled by the desired visited network VPLMN or an overload condition might even be caused in the visited network VPLMN. Since it cannot be ensured that these two problems might occur, the national roaming service is in most cases not used. Furthermore, the mobile station may not have the permission to use national roaming at all. The same problem can occur if the operator is operating several networks that overlap and the mobile stations have multi-band functionality, e.g. GSM 900/1800.
Furthermore, there may exist other situations and conditions in the home network which may require a flexibility to at least temporarily use services from one or more other networks. For example, one or a plurality of users served by an MSC may have to be transferred only temporarily to another network if a MSC undergoes maintanence. Therefore, many conditions in the home network may require the flexible access to services of another network.
The invention has been devised to overcome the disadvantages described above in the current GSM standards relating to the national roaming service. In particular, it is the object of the invention
to provide a method, an exchange, a telecommunication system and a mobile station, such that mobile users can be provided with a flexible access to services of several networks.
This object is solved by a method according to claim 1. Furthermore, this object is solved by a telecommunication system according to claim 21. Furthermore, this object. is solved by an exchange according to claim 37. The object is also solved by a mobile station according to claim 46.
According to the invention, the switching means of the (first) home network and the switching means of the (second) visited network perform an exchange of request and response messages when a predetermined condition, e.g. an overload condition, occurs in the home network. Thereby, the home network and the visited network negotiate as to whether or not the visited network is capable of handling traffic for one or more mobile stations of the home network, which cannot be handled in their own network. In particular, the switching means of the visited network returns a response message to the switching means of the home network to indicate whether or not it will and can grant an access to a particular number of mobile stations of the home network. Those mobile stations which have been indicated can then be registered in the visited network and are therefore guaranteed a flexbile access in the network. Thus, the national roaming can be controlled on a gradual basis and it is avoided that mobile stations are granted access merely on a statistical basis as in the conventional national roaming service. At the same time the access is granted without causing an overload in the visited network.
Preferably, the request message sent by the switching means of the home network to the switching means of the visited network can contain the number of mobile stations and/or the access classes of the mobile stations and/or information about the overloaded area in said home network. Thus, the switching means of the visited network can advantageously decide whether or not it has the capacity to handle a particular set of mobile stations.
Preferably, the request message is sent to two or more switching means of the visited network. Since the traffic conditions may vary among several switching means of the visited network, the success rate of transferring a large number of mobile stations to the visited network can thus be increased. Furthermore, the several switching means may respectively take over a certain number of mobile stations for a predetermined access class of mobile stations, such that the increased load in the visited network can be distributed amongst a plurality of switching means.
If several second networks are provided which can potentially take over a certain number of mobile stations, the request message may also be sent simultaneously to one or more switching means in each visited network. This can achieve an even load distribution amongst a plurality of visited networks.
The switching means of the home network may also advantageously determine on the basis of the access classes, to which switching means or second network the request message should be transferred. Since some visited networks may provide special functionalities for mobile stations of a particular access class, the switching means of the home network can advantageously attempt to transfer mobile stations of a particular access class to a second network which has been specifically adapted for handling such an access class. Furthermore, the switching means of the home network may also send several request messages each containing a particular number of mobile stations of a particular access group separately to several different switching means in one visited network.
Preferably, the switching means of the home network may send an overload message to the base station controllers of the home network indicating that a roaming is allowed for one or more mobile stations, preferably according to a particular access class. The base station controller can thus transfer the overload message to the respective mobile stations indicated therein, preferably to all mobile stations of a particular access class.
Preferably, the overload message indicates the visited network and/or a particular switching means within the visited network, to which the indicated mobile stations are allowed to roam. In particular, when the switching means of the home network receives several response messages from several switching means located in one or more visited networks, then a plurality of overload messages can be transferred to subgroups of mobile stations, wherein each subgroup or access class will receive an indication to which visited network and/or switching means the mobile stations are allowed to roam. Thus, particular groups of mobile stations of the home network, possibly located in the same location area or in a different location area, may be transferred to the same or the different local area in the visited network.
Preferably, a copy of the subscriber data of the mobile stations which cannot be handled by said first network stored in the home location register of the first network is sent to the switching means of the visited network. Thus, the mobile station which cannot be handled in the first network, obtains an access in the visited network.
When the mobile station has been registered in the visited network and can communicate using the switching means of the visited network, the mobile station can also perform repeated re-registering requests to re-register in the switching means of its home network, such that the mobile station may be advantageously re-registered in its home network even before a stop message indicating the end of the overload condition is received from the switching means of the home network.
When a mobile station has been registered in the visited network, the switching means of the visited network can determine allowable location areas or cells in said visited network, in which said mobile station is allowed to roam. Since the overload condition may not prevail for an unlimited period of time, there is thus no need to allow the transferred mobile station to occupy resources in all cells of the visited network, such that the transferred mobile station does not present an additional load in all cells of the visited network.
When the mobile station moves outside said allowable location area, the switching means of the visited network may either continue the call, perform an inter-network handover to the home network or to yet another visited network or it may release the call which the transferred mobile station carries out. Thus, a suddenly increasing load in other cells which may be heavily occupied can be avoided.
When several visited networks are provided, the switching means of the home network can scan several visited networks if a first visited network has refused to take over the mobile station during the overload condition. The switching means of the home network may also negotiate with the respective switching means of several visited networks which second network is to take over a particular number or a particular access class of mobile stations. Thus, the switching means of the visited network can scan several visited networks until all mobile stations which can not be handled due to the overload condition will be taken over by one or more visited networks.
When it is detected that the overload condition has ended in the home network, the switching means of the home network sends a stop message to the visited network whereupon the switching means of the visited network withdraws the access permission for the mobile stations. The mobile stations then re-register in their home network, preferably at the same switching means from which they have left the home network. Of course, if the mobile station has roamed to another cell due to a distance movement, then the mobile station might re-register at a different switching means from which it has originally departed.
Preferably, the subscriber data in the switching means (visitor location register) in the visited network is canceled only after location information contained in an update location information message is checked against the location information in the home location register stored when the subscriber was registered in the visited network. This ensures that the subscriber data stored in the visitor location register of the visited network is only canceled when the mobile station is successfully re-registered in its own home network, such that the mobile station will never end up in a condition where it is not registered anywhere.
A mobile station can preferably receive an overload message from a base station controller which indicates that an overload condition has occurred in the home network and for indicating to said mobile station another visited network which has agreed to take over the communication for said mobile station as long as the overload condition prevails. Since such an overload message already indicates a visited network which has agreed to take over the communication, the mobile station can then transfer to this visited network such that it can be guaranteed that the mobile station has an access in the visited network.
Preferably, the overload message received by the mobile station contains information indicating allowable location areas in the visited network. Thus, extensive loads in particular cells can be avoided.
Furthermore, when the mobile station receives a release message from the switching means of the visited network after the overload condition has ceased in its home network, the mobile station may also send a request to the switching means of the visited network to request a transfer to yet another visited network or another particular switching means of the home network. The mobile station may also indicate a particular mobile service switching center of its own home network, such that advantageously a particular switching center can be selected.
Hereinafter, embodiments of the inventions will be described with reference to the attached drawings.